Abstract
The compositional simulator of Pope and Nelson has been extended to include a number of additional effects. The efficiency of the oil displacement has been calculated as a function of slug size, polymer drive size, surfactant and oil concentrations in the slug, slug/oil bank and drive/slug mobility ratios, surfactant and polymer absorption, interfacial tension (IFT), phase type, binodal curves, plait point location, capillary desaturation curves for each point location, capillary desaturation curves for each phase, relative permeabilities, waterflood residuals, phase, relative permeabilities, waterflood residuals, dispersion, electrolyte gradient, and amount of surfactant injected. High-concentration slugs in a Type II (+) (or plait point left) phase environment were found to be less dependent on low IFT than low-concentration slugs or slugs in a type II (-) phase environment. For the Type II (-) case, oil phase environment. For the Type II (-) case, oil recovery is not sensitive to plait point location. However, the best oil recovery for a given amount of injected surfactant occurs where a salinity higher than optimal exists downstream of the slug and a salinity lower than optimal exists upstream of the slug (in the polymer drive) and the slug itself traverses as much of the reservoir as possible in the low-tension Type III environment. The low final salinity promotes low final retention of surfactant. For the cases studied, the salinity, surfactant concentration, oil concentration, and polymer concentration of the slug itself then made relatively little difference.
Introduction
Several authors have examined one-dimensional simulation of surfactant flooding and the various complex compositional effects that occur during the displacement of oil with surfactants and polymers. Nelson and Pope presented laboratory results showing the importance of the Type III phase environment and how oil recovery can result from mechanisms other than low IFT. Actually, several key phenomena affecting oil recovery are strongly coupled and need to be considered simultaneously both to understand and to simulate the process. The simulator of Pope and Nelson was a first attempt to model these effects, which include IFT, phase behavior, fractional flow, adsorption, and polymer properties as a function of electrolyte. Ion exchange properties as a function of electrolyte. Ion exchange has been shown to have an important impact on the process as well, since the electrolyte environment process as well, since the electrolyte environment affects many of the most important fluid properties involved. Pope and Nelson have shown how the displacement of oil is "miscible-like" under certain conditions, even when dispersion and adsorption are considered and small slugs are used. However, to be practical, a very carefully designed electrolyte practical, a very carefully designed electrolyte gradient must exist (or some other equivalent gradient of another variable such as surfactant molecular weight, alcohol, etc.). Here we continue the investigation of these process variables by presenting results of a sensitivity study. Both presenting results of a sensitivity study. Both water and oil-rich surfactant slug cases are simulated.
Model Changes
Pope and Nelson presented a description of the Pope and Nelson presented a description of the original simulator. Several changes that have been made will be discussed briefly. The IFT functions are now those proposed by Healy and Reed.
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SPEJ
P. 357
Capillary Desaturation in Unconsolidated Beads